1. Field of the Invention
This invention resides in the field of biochemical laboratory equipment, and particularly equipment that is used for analyses of multitudes of small samples of biologically derived mixtures.
2. Description of the Prior Art
Many biochemical laboratories perform procedures that involve analyses of large numbers of samples, each containing biological species that are very similar in structure and each available only in very small quantities. Analysis of this kind are performed in a sequence of stages, each stage requiring close control of the reaction conditions while maintaining individual handling of each sample. To accomplish this, the samples are often arranged in two-dimensional arrays, and sophisticated instrumentation, frequently involving robotics, is used to remove individual samples from an array and transport the samples to various stations where the different stages of the procedure are performed. Proteomics is an example of such a procedure. The species to be isolated in proteomics typically reside in spots on a two-dimensional gel or on a membrane to which the spots have been transferred from a gel. Polyvinylidene difluoride (PVDF) and nitrocellulose are examples of materials from which such membranes are made. The individual stages in a proteomics procedure include imaging of the array and location of the spots, plus excision of the spots from the array, transfer of the excised spots to various locations, digestion of the substances contained in the spots, and analysis of the digested substances, all performed by the instrument under computer control. The digestion and analysis steps are typically performed in the wells of a multi-well plate such as a 96-well microplate, and excision of the spots from the membrane and transfer to the wells are performed by an automated spot cutter which is controlled by the robotics. A typical spot cutter is a hollow cylinder that is approximately the size of a hypodermic needle. The cylinder is movable in the x-y plane for positioning over individual spots, and in the z-direction to be lowered onto the gel or membrane to cut a very small disk containing the spot from the gel or membrane. Disclosures of robotics-containing instrumentation for performing this task are found in International Patent Publication No. WO 99/15875, MacQuarie Research Ltd., applicant, publication date 1 Apr. 1999 (“Apparatus for Removing a Sample From an Array of Samples and a Cutting Tool for Use With That Apparatus”); and International Patent Publication No. WO 00/57153, Campbell Corporation Pty. Ltd., applicant, publication date 28 Sep. 2000 (“Improvements in Apparatus and Method for Removing Samples”). An example of instrumentation that incorporates disk-excising robotics is the 2DiD integrated system for imaging and spot-picking of LEAP Technologies (Carrboro, N.C., USA). When the disk is to be cut from a membrane support material such as PVDF or nitrocellulose, the cylinder in certain instruments is rotated during the cutting operation to facilitate the cutting of the membrane by the cylinder edge. The above-referenced Publication No. WO 00/57153 discloses a “belt and pulley arrangement” for accomplishing this rotation.